The present invention relates to light transmitting optical fiber device. More particularly, the present invention relate to a light transmitting optical fiber device having its light radiating end shaped and constructed in a specified fashion and which can advantageously be used in an optical display system.
A related art optical display system using an array of multiple optical fibers is shown in Japanese Patent Application Laid Open No. 198406/1984. In this system, optical fibers with their light radiating end surfaces formed perpendicular to the fiber axes are embedded in a certain array in a display panel and are bundled together at the other end which faces a light source. Each of the optical fibers with their light radiating end faces being perpendicular to the fiber axes has such a small diameter (10 .mu.m to a few mm) that the total cross-sectional area of the fibers that occupy the area in which a display is to be made is inevitably very small, and in order to fabricate an optical display unit having a desired display area, a huge number of optical fibers must be employed. Another problem associated with the use of optical fibers having their light radiating surfaces cut perpendicular to the fiber axes is that even if the fibers are made of or plastics, the angle of light radiation form the fiber ends is not more than .+-.30.degree. with respect to the optical axis and the resulting optical display is highly directive, rather than featuring a wide visual angle.
Optical fiber display systems that are designed to maximize the area of display surface are shown in Japanese Patent Application Laid Open Nos. 86709/1986, 71782/1986 and U.S. Pat. No. 4,116,739. The optical fiber array portion of these display systems is shown in FIG. 4 (perspective view) and in FIG. 5 (a cross-sectional view). Multiple optical fibers (41) arranged in the two directions of y-and z-axes are positioned to face a light source at one end so as to form an image receiving surface (44), with other end of the fiber array being inclined to the x-axis direction of fiber axis so as to provide an enlarged display surface (45). As shown in FIG. 4, an incident image (42) is displayed as an enlarged image (43) on the surface (45). As shown in FIG. 5, each of the incident rays (56) that encounter the image receiving surface (44) is guided through an individual optical fiber (51) in the direction of the arrow as it undergoes repeated internal reflection without escaping to the outside of the fiber, and emerges from the display surface (45). In this type of optical display system, the total cross-sectional area of the display surface is large compared with the total cross-sectional area of the image receiving surface so that the images provided by the individual fibers are not bright enough to produce a sharp overall display.
As shown in FIG. 6(A), the angle of light radiation from an end (62) of an optical fiber (61) that is perpendicular to the fiber axis covers the range of .+-.30.degree.. If the optical fiber has a light radiating end (63) which, as shown in FIG. 6(B), is inclined to the fiber axis, rays of light radiating from this end have high directivity in the direction of the fiber axis as illustrated by (64) and (65), with the result that the visual angle of the display system becomes narrower than in the case shown in FIG. 6(A). As a further problem, some of the rays of light propagating through the optical fiber (61) are reflected by the inclined radiating face (63) and the reflected ray (66) leaks from the fiber (61) by passing through the fiber wall (67) that is situated below the imaging surface. Because of this optical loss, the quantity of light radiating from the imaging surface is insufficient to produce a bright display.